1. Field of the Invention
The invention relates to devices and methods for removing tissue from body passageways, such as removal of atherosclerotic plaque from arteries, utilizing a rotational atherectomy device.
2. Description of the Related Art
A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in a patient's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (under the endothelium) of a patient's blood vessels. Very often over time, what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Rotational atherectomy procedures have become a common technique for removing such stenotic material. Such procedures are used most frequently to initiate the opening of calcified lesions in coronary arteries. Most often the rotational atherectomy procedure is not used alone, but is followed by a balloon angioplasty procedure, which, in turn, is very frequently followed by placement of a stent to assist in maintaining patentcy of the opened artery. For non-calcified lesions, balloon angioplasty most often is used alone to open the artery, and stents often are placed to maintain patentcy of the opened artery. Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience stent restenosis—i.e., blockage of the stent which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent. In such situations an atherectomy procedure is the preferred procedure to remove the excessive scar tissue from the stent (balloon angioplasty being not very effective within the stent), thereby restoring the patentcy of the artery.
Several kinds of rotational atherectomy devices have been developed for attempting to remove stenotic material. In one type of device, such as that shown in U.S. Pat. No. 4,990,134 (Auth), a concentrically shaped ellipsoidal burr covered with an abrasive abrading material such as diamond particles is carried at the distal end of a flexible drive shaft. The burr is rotated at high speeds (typically, e.g., in the range of about 150,000-190,000 rpm) while it is advanced across the stenosis. As the burr is removing stenotic tissue, however, it blocks blood flow. Once the burr has been advanced across the stenosis, the artery will have been opened to a diameter equal to or only slightly larger than the maximum outer diameter of the burr. Frequently, since the burr is of a fixed resting diameter, more than one size burr must be utilized to open an artery to the desired diameter.
U.S. Pat. No. 5,681,336 (Clement) provides an eccentric tissue removing burr with a coating of abrasive particles secured to a portion of its outer surface by a suitable binding material. This construction is limited, however because, as Clement explains at Col. 3, lines 53-55, that the asymmetrical burr is rotated at “lower speeds than are used with high speed ablation devices, to compensate for heat or imbalance.” That is, given both the size and mass of the solid burr, it is infeasible to rotate the burr at the high speeds used during atherectomy procedures, i.e., rotational speeds within the range of about 20,000-200,000 rpm. Essentially, the center of mass offset from the rotational axis of the drive shaft would result in development of significant and undesirable centrifugal force, exerting too much pressure on the wall of the artery and creating too much heat and excessively large particles. As with Auth, the burr size is fixed and may require using more than one size burr to open the subject lumen to the desired diameter.
U.S. Pat. No. 6,132,444 (Shturman) and U.S. Pat. No. 6,494,890 (Shturman) both commonly assigned, disclose, inter alia, an atherectomy device having a drive shaft with an enlarged eccentric section, wherein at least a segment of this enlarged section is covered with an abrasive material. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery. The device is capable of opening an artery to a diameter that is larger than the resting diameter of the enlarged eccentric section due, in part, to the orbital rotational motion during high speed operation. The orbital rotational motion is primarily due to the offset of the center of mass of the enlarged eccentric section from the drive shaft's rotational axis. Since the enlarged eccentric section may comprise drive shaft wires that are not bound together, the enlarged eccentric section of the drive shaft may flex during placement within the stenosis or during high speed operation. This flexion allows for a larger diameter opening during high speed operation, but may also provide less control than desired over the diameter of the artery actually abraded. The disclosure of U.S. Pat. Nos. 6,132,444 and 6,494,890 are each hereby incorporated by reference in their entirety.
Other techniques and devices have been proposed to generate a rotational sweeping diameter that is greater than the resting diameter of the abrasive section. Generally, these devices include a pre-bent guide wire that will, when placed within the lumen of a rotational drive shaft, create a bend in the drive shaft at the abrasive region. When the guide wire is removed, the drive shaft returns to its normal uncurved and substantially linear shape. Such an arrangement will, when the pre-bent guide wire is in place, create a sweeping diameter for the abrasive region of the drive shaft that is greater than its resting diameter. Examples of such pre-bent guide wire proposals include U.S. Pat. Nos. 5,312,427, 5,356,418, 5,554,163 all to Shturman and commonly assigned with the present application, the disclosure of each being incorporated herein by reference insofar as they disclose a drive shaft is urged into a curvilinear profile by virtue of the presence of the curved guide wire within the drive shaft's lumen. Other examples include U.S. Pat. No. 5,548,843 to Wulfman and U.S. Pat. No. 6,156,046 to Passafaro.
The pre-curved guide wire designs each require the guide wire to be in place within the lumen of the drive shaft to create the desired bending of the drive shaft and abrasive region which may hamper flexibility of the drive shaft during high-speed rotation. Further, the pre-curved guide wire approach may find difficulty in traversing the often tortuous vasculature enroute to the stenosis of interest. Moreover, the pre-curved guide wire devices are not designed for focused directional ablation.
Thus, it would be highly advantageous to provide an atherectomy system, device and method that is substantially linear upon entry into the patient's vasculature but at the same time allows for directional abrading and/or cutting within a lumen as well as the possibility of expansion of the sweeping diameter of the spinning drive shaft's abrasive region based, at least in part, upon pre-bending of the drive shaft itself, not the guide wire as previously proposed.
The present invention addresses, inter alia, these needs.